Tonight, as fans mourn the death of comedy icon robin Williams, nowhere is the loss more keenly felt than at home by his beloved family. But why would on-line bullies target one of his children? All three bravely stepping forward today sharing their pain. And the way his daughter, Zelda Williams responded, will make you smile. They were often in the background for a man whose shadow was larger than life itself. There they are playing at robin Williams's side. For robin Williams, his three children were the greatest gift he ever received. If you could go back and relive any day in your life? Just the birth of my children, each one. Those are all great days. And they have all turned out amazing. That is the ultimate production deal. That is the gift that keeps on giving and that is the thing that makes life worth living. Reporter: Today, Zelda, now 25, offered a rare look on a post. My family has always been private about our time spent together, it was our way of keeping one thing that was ours with a man who we shared with the entire world. But now that is gone and I feel stripped bare. I am robin Williams, this is my daughter, Zelda ray Williams. Reporter: Though they were close, it was obvious they shared a loving bond. Robin tells the story how he named his little girl. It is Zelda for the legend of Zelda. Reporter: They even starred in a commercial for her namesake. I saved your kingdom. Dad? Zelda. Are you mixing me up with the princess again? Hard to say, you're both pretty magical? Indeed, while the world is still grieving, the question is still harder to bear. While I will never understand how he could be loved so deeply and not find it in his heart to stay, there is some comfort in knowing that so many share his love. There is a lot of anger, shame, blame, if I had been a better friend, wife, mother, sister, would this still have happened? And today, Zelda had even more to deal with taking herself off Twitter after on-line bullies baited her with disturbing doctored images of her father. But she responded with her father's good humor. As for those who send negativity you know that some small part of my dad is sending a flock of pigeon to poop on your car, after all, he loved to laugh. You know, that is out of line. Her brothers, Zach, 31, and 22-year-old Cody shared their grief publicly as well. The world got a little grayer, I will carry him with me every day and will look forward forever to the moment when I get to see him again. His struggles were theirs, too, living with a genius father fighting addiction. In 2006, he spoke to Diane sawyer about going home to his family after he was finally sober. What have they said to you through this? That they love me, simply, the bottom line, and then the rest is up to me, and god, and you got to keep working it every day. That is the drill. Humiliations give you humility, really. Is there a sadness about the past two years? Yes, there is a sadness and also hope. Sadness, you wish they hadn't happened but they did and the purpose is to make you different. It is what you call a buddhist gift. I would call it a Christian gift, it's your back, the thing you realize what matters are others way beyond yourself. But today we learned that just days before Williams' death, his biking partner was scared for his friend. Our last ride ten days ago was very different. He barely spoke on the ride. He was very distracted and stressed. We didn't play around much before and we didn't play around much after or on the ride. He went so far to alert Williams' manager. They were aware of it and doing everything they possibly could. But yeah, that was the robin Williams I had never seen before in all the years I had known him, and probably not too many had seen him. Skippy, lo Y rpy -- skinny, lost a lot of weight, I was very worried. We wanted you to choose us based on your age. Just two months later, robin Williams was back in rehab. The sadness and depression that plagued robin Williams is all too common in Hollywood. There is a pressure put on stars 24 hours a day that people who were famous in previous generations just didn't have to deal with. I went to rehab in wine country just to keep my options open. Stand-up comics have a lot of struggles in particular, they are out there, not playing a character and that comes with a lot of pressure. When you're a celebrity, everybody wants a piece of you. In a chilling scene in his break-out role of Mork and Mindy. Some are victims of their own fame, very special and talented people, people like Elvis Presley, Marilyn Monroe, Janis Joplin, jimmy Hendrix, and John Lennon. In all his roles, to the cross-dressing nanny, there was also pain behind the laughter, he spoke openly to NPR in 2006. In the process of comedy you have to look at it completely honestly, and then, on the other side you will be looking under the rock occasionally for the laughter, so there is a depressed side, but is it always? No. The radio host asked if he was depressed? Not clinically, no. The sadness is one that many seem to share, Richard Pryor, John belushi, also hid sadness behind the joke. A lot of human experience can be very painful. And laughing about it, joking about it is a coping mechanism, it is just not a very good one. Because it can mask it but it doesn't really heal it. Two days after Williams' death the outpouring of love and grief continues, tonight, a tribute for the man who made it his mission to bring us laughter and tears. A fitting memorial.

This transcript has been automatically generated and may not be 100% accurate.

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